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I have set $x = {1,2,3,4,5}$ and set $y = {2,3,4,5,6}$. Lets say the correlation of $x$ and $y$ is $0.7$. If I then have set $z = {1,2,3,4,5,2,3,4,5,6}$, and I do autocorrelation using lag $=$ $5$, should I not get the same $0.7$? I have been doing this but I keep getting different results. I'm wondering if I'm doing something wrong, or maybe it is that they should have different results.

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The first question is probably answered at stats.stackexchange.com/q/10947 . – whuber Jun 2 '11 at 3:13
Thanks guys that answers question one. – solartic Jun 2 '11 at 4:02
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Please don't ask two separate questions in one. @zbicyclist Please use answers for answers. – mbq Jun 2 '11 at 8:15

1 Answer

up vote 1 down vote accepted

denominators are different in the correlation formula and the autocorrelation formula. (moved to answer at moderator's request)

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The explanation for the difference is provided at stats.stackexchange.com/questions/10947/… – Rob Hyndman Jun 3 '11 at 8:38

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